1. Technical Field
The present disclosure relates to a display device, and more particularly, to a source driver capable of removing scan line noise and a display device having the same.
2. Discussion of the Related Art
FIG. 1 is a block diagram of a conventional display device 100. The display device 100 includes a display panel 110 having liquid crystal cells 111 that are arranged in the form of a matrix where gate lines G1 through GQ intersect source lines Y1 through YP; a gate drive 120 that drives the gate lines G1 through GQ; and a source driver 130 that drives source lines Y1 through YP. Each of the liquid crystal cells 111 includes a switch 112 connected to a corresponding gate line and a corresponding source line, and a liquid crystal (not shown).
The display device 100 uses a sequential line driving method in which an image is displayed by sequentially driving the gate lines G1 through GQ. When the gate driver 120 supplies a driving signal to one of the gate lines G1 through GQ, all switches (not shown) connected to the gate line are turned on. Signals transmitted from the source driver 130 to the source lines Y1 through YP are supplied to a pixel electrode VPIX corresponding to the switch turned on by the gate driver 120 via the switches.
The supply of the signals to the pixel electrode VPIX causes an electric field to occur between the pixel electrode VPIX and a common electrode VCOM, and the electric field changes the orientation of the liquid crystal in the corresponding liquid crystal cell 111, thus displaying an image. The crystal cell 111 further includes a storage capacitor CST to maintain a signal supplied to the pixel electrode VPIX until a gate line is driven for a next frame. There is also some capacitance associated with the liquid crystal.
If an electric field is maintained in a liquid crystal cell, which is controlled by an electric field, in the same direction, the liquid crystal in the liquid crystal cell is degraded, thus causing performance degradation. Accordingly, a polarity of a pixel electrode with respect to a common electrode must be inverted at predetermined intervals of time so as to change the direction of the electric field applied to the liquid crystal cell.
Therefore, a frame inversion method, a line inversion method, a column inversion method, and a dot inversion method have been introduced. In the case of the frame inversion method in which the direction of an electric field is changed for each frame, however, the electric field is maintained in the same direction until a frame is scanned, and thus, a leakage current is generated from a switch, thus lowering a level of a signal to be supplied to a liquid crystal cell.
In the line inversion method, pixels have the same polarity in a horizontal direction, thus causing cross talk in the horizontal direction. In the column inversion method, cross talk is present in the vertical direction, and a high-voltage source driver is needed to respectively supply signals having different polarities to adjacent source lines.
In the dot inversion method, since all adjacent pixels have different polarities, the cross talk can be solved and the image quality improved, but a high-voltage source driver is needed and power consumption is increased.
A multi-line inversion method or a multi-dot inversion method has been introduced to solve these problems. The multi-inversion method includes a 2H-inversion method in which signal polarity is changed every two horizontal periods, wherein the horizontal period indicates a period during which a gate line is driven.
FIGS. 2A and 2B are waveform diagrams of source line driving signals SIC_ODD and SIC_EVEN, a gate line driving signal GIC, a common electrode signal VCOM, and a first output control signal CLK1 in a conventional display device that is driven by a sub-dot pattern. The first output control signal CLK1 is also referred to as a load signal or a data latch signal according to source driver manufacturing companies.
Referring to FIGS. 2A and 2B, during an odd-numbered active (high-level) period of the first output control signal CLK1, a charge sharing operation C/S is performed to equalize the voltage of the odd-numbered source line driving signal SIC_ODD with that of the even-numbered source line driving signal SIC_EVEN. The source driver is maintained at a high-impedance state H1_Z during an even-numbered active period of the first output control signal CLK1.
The source line driving signals SIC_ODD and SIC_EVEN are supplied to source lines in response to a falling edge of the first output control signal CLK1.
When the two source line driving signals SIC_ODD and SIC_EVEN are output in an even-numbered horizontal (2H) period, voltage levels are changed in the same direction, thus causing common voltage noise NOISE. Further, the source line driving signals SIC_ODD and SIC_EVEN coupled to common voltage VCOM are affected by the common voltage noise NOISE.
As illustrated in FIG. 2A, there are no problems when a common voltage noise NOISE is low. As illustrated in FIG. 2B, however, when a common voltage noise NOISE is increased due to an external compensation circuit or the arrangement of power lines in a panel, the source line driving signals SIC_ODD and SIC_EVEN are coupled to the common voltage noise NOISE. Thus, the levels of the source line driving signals SIC_ODD and SIC_EVEN do not reach a saturation state until a gate line driving signal (GIC) 203 is supplied in the 2H period after inversion.
Accordingly, the different between an (A) region charged by supplying a gate line driving signal 201 in an 1H period, and a (B) region charged by supplying the gate line driving signal (GIC) 203 in the 2H period while the levels of the source line driving signals SIC_ODD and SIC_EVEN do not reach the saturation state, is caused. That is, the difference between the charging rates of the two consecutive gate line driving signals (GIC) 201 and 203 is caused. In this case, scan line noise, that is, a wave pattern in which a dark line and a light line alternately recur, is generated.